In the prior art, it is known to produce aluminum in coil form from a continuous casting apparatus wherein molten aluminum is delivered from a tundish and cast in the form of a metal sheet or strip and rolled into a coil on a coiler. Generally, in this process, molten aluminum is deposited on a moving chill surface from a tundish having an open outlet. An inlet is provided for the flow of molten metal into the tundish from a source of molten metal. The direct casting of the molten aluminum metal onto a chill wheel, preferably a grooved chill wheel, produces a cast aluminum product at a rapid rate. The aluminum cast strip is wound on a coiler in heated form, generally at a temperature in the range of about 900.degree. F.
Drag casting apparatus and methods of this types are described, for example, in U.S. Pat. Nos. 4,828,012, 4,896,715, 4,934,443, 4,945,974, 4,940,077 and 4,955,429. The disclosures of these patents are hereby specifically incorporated by reference with respect to the method and apparatus for the production of aluminum strip and coil from molten aluminum or aluminum alloys.
In order to properly coil the as-cast strip or further work the cast strip into a product having satisfactory quality, it is important to provide a cast strip leaving the casting surface having a proper shape or cross-sectional profile.
Difficulties have been encountered in prior art processes in achieving acceptable cast strip cross-sectional profiles in drag casting of aluminum products. Delivering molten aluminum from a tundish onto a moving chill surface produces a sheet product having an increased thickness at the edges thereof. This increased thickness is a result of a faster cooling rate at the edges of the chill surface and a corresponding "dog-bone" effect, or washboard or wavy edge. This condition prevents effective coiling of the cast strip as well as difficulties in further reducing the cast strip in subsequent rolling operations. Cold rolling of sheet or strip product generally requires that the sheet or strip have a slightly thicker center portion than edge portion. Strip having a "dog bone" shape generally has thick edge portions and a thinner crown section.
In the prior art, various devices have been proposed in conjunction with direct casting apparatus for improved continuous cast strip profile and gauge. In U.S. Pat. No. 4,828,012 to Honeycutt, III et al., diffusion means are provided in a tundish structure to produce a substantially uniform flow rate through the tundish and across its width as molten metal approaches a chill surface. The tundish also includes a flow control gate mounted for vertical sliding movement between sidewalls of the tundish. The gate is adapted to be moved from a lowered position which prevents flow of metal to the exit lip of the tundish to a raised position out of contact with the molten metal to permit free flow to the chill casting surface.
U.S. Pat. No. 4,940,077 to Honeycutt, III et al. is drawn to a direct metal strip casting apparatus wherein the width of the strip being cast may be changed without interrupting the casting operation. This patent also discloses adjustable or moving baffles to compensate for any flow pattern change resulting from the insertion or removal of the width changing device.
U.S. Pat. No. 4,955,429 discloses another direct casting apparatus. In this patent, the tundish is provided with flow distribution diffusers to control and diffuse the flow of molten metal to provide substantially uniform temperature across the width of the tundish at the outlet. This patent indicates that, in casting aluminum strip having a nominal thickness of about 0.040 inches, a temperature variation of 10.degree. F. in the tundish will result in a strip thickness change of approximately 0.001 inch.
Devices have also been proposed for control of molten metal flow in tundishes associated with dual-roll continuous casting machines. Each of U.S. Pat. Nos. 3,799,410 to Blossey et al. and 4,550,767 to Murrysville et al. disclose fixed baffle means to facilitate control of the flow of molten metal in a tundish prior to continuous casting. In U.S. Pat. No. 4,865,115 to Hirata et al., a twin roll continuous casting apparatus is disclosed having opposing core sections forming a slit nozzle. One core section is held stationary with the other core section being supported as to move toward or away from the stationary core section to adjust the distance between the core sections. The movable core section permits adjusting the width of the slit nozzle and consequently controlling the flow rate of melt through the nozzle.
U.S. Pat. No. 4,591,135 to Fosnacht et al. discloses another tundish for continuous casting of molten metal having a dam which provides uniform residence times in the tundish prior to molten metal exiting the tundish. A fluid flow control structure is located between the dam and the tundish sidewalls to avoid a dead zone area in the tundish.
Disadvantages of prior art devices associated with tundishes and control of molten metal flow in continuous casting processes include inability to maintain precise control across the width of the cast strip. As such, a need has developed to more effectively control the flow of molten metal in the tundish prior to the molten metal contacting the casting surface for improved strip profile and gauge control.
In response to this need, the present invention provides an adjustable flow control device which permits precise control over the molten metal flow patterns in a tundish. Capability of maintaining a desired gauge consistency and thickness profile is provided by control of the adjustable flow control device in response to sensed casting variables during the continuous casting operation.
None of the above-listed documents teach or fairly suggest an adjustable flow control device for continuous casting of metal strip that comprises a plurality of adjustable baffles that extend across the width of a tundish.